1. Field of the Invention
The field of the invention relates to shield systems for protecting against needle sticks, and syringes including such systems.
2. Brief Description of the Related Art
Syringes are well known medical devices for administering medicaments to patients. They are also used for other well known purposes in the field of medicine. Prefilled syringes are generally considered as those which are filled with a selected dosage of medicament or other substance by a pharmaceutical manufacturer for distribution to the end user. They are often comprised of a glass or plastic barrel which contains the medicament or other substance and a piston slidably mounted within the barrel. One end of the barrel includes a needle or the like affixed thereto or a connector for a needle assembly such as a Luer fitting. The term xe2x80x9cneedlexe2x80x9d as used herein should accordingly be construed broadly to include various types of piercing elements or connectors, whether sharp pointed or blunt. The other end of the syringe is open to allow the insertion of a plunger rod. The plunger rod allows the user to apply manual force to the piston, causing the medicament to be delivered through the needle or other piercing element.
The use of a sharp-pointed piercing element entails the risk of accidental needle stick. To avoid such accidents, many prior art hypodermic syringes have included rigid cylindrical safety shields telescoped over the syringe barrel. These shields can be moved between retracted positions where the needles are exposed for use, to extended positions where the needles are surrounded by the shields. U.S. Pat. Nos. 4,425,120, 4,573,976, 4,850,994 and 4,923,447 disclose various shield systems for hypodermic syringes. The latter two patents disclose shields which are spring-actuated. It is ordinarily desirable to lock the needle shields in the protected positions, and a number of prior art designs provide for such locking. Some systems, such as those disclosed in U.S. Pat. Nos. 5,201,708, 5,242,240 and 5,318,538 are designed to allow the shields to be retracted from their locked, extended positions.
A shield system for protecting the piercing element of a prefilled syringe is disclosed in European Publication No. EP 0 740 942 A1. The disclosed system includes a holder which is coupled to the flange of the syringe barrel, and a shield which is telescopically mounted to the holder. Two hands are required to operate this system.
The invention relates to a safety shield system for a syringe, and such a system as used in combination with an assembly capable of functioning as a syringe. In accordance with the preferred embodiments of the system, the user is able to cause the shielding of a needle by simply applying pressure to the plunger rod of the syringe following injection of the contents of the syringe barrel. The shield may accordingly be deployed automatically through the use of only one hand. As there is no need to place the hand near the needle for any purpose, the risk of needle stick injury is reduced.
In accordance with the objects of the invention, a medical device is provided which includes an automatically operable shield system mounted to a syringe barrel. The system includes a holder which defines an enclosure. The syringe barrel extends at least partially, and preferably almost entirely, within the enclosure. The barrel is slidable within the holder. A retaining member is positioned on the holder, and is engageable with the barrel. This member prevents the barrel from being uncoupled from the holder. A shield is mounted to the holder, and positioned about at least a portion of the barrel. The shield is axially movable with respect to the holder between retracted and extended positions. It is intended to cover the needle tip when in the extended position. A spring engages the shield, and urges it towards the extended position. A first stop member is positioned on the shield, and a second stop member is positioned on the holder. The second stop member is engageable with the first stop member when the shield is in the retracted position. The force of the spring, by itself, is insufficient to cause disengagement of the first and second stop members. The barrel is operationally coupled to the shield such that sufficient axial movement of the barrel causes axial movement of the shield sufficient to cause disengagement of the first and second stop members. Such movement of the barrel is ordinarily caused by pressure exerted on the plunger rod by the user of the syringe following complete injection of the contents of the barrel. Upon disengagement of the first and second stop members, the spring causes the shield to move to the extended position.
The proximal end of the holder is preferably adapted to engage and retain the flange which may be present at the proximal end of the syringe barrel. The axial movement of the shield is preferably limited by a set of locking detents formed on the holder. Such movement could alternatively be limited by a tether connecting the holder and shield. The shield is preferably positioned within the holder such that the spring engages the first stop member. The opposite end of the spring can bear against any suitable surface, such as the flange on the syringe barrel, if present, or a collar portion of an end fitting slidably positioned within the holder.
The shield system according to the invention is comprised of a holder, a shield, a spring and, preferably, an end fitting. The holder is adapted for receiving at least a flanged portion of the barrel of a syringe, and includes axially spaced, opposing abutment surfaces to retain the flange. The distance between these surfaces corresponds to the distance the syringe can be axially moved with respect to the holder once mounted thereto. The shield is slidably mounted to the holder, and is movable between retracted and extended positions. A spring urges the shield towards the extended position. The holder includes a stop member which is engageable with the shield to maintain it in the retracted position. Sufficient axial movement of the shield causes disengagement of the stop member, allowing the spring to move the shield to the extended position. An end fitting is preferably incorporated in the system to maintain the position of the spring prior to insertion of a syringe into the holder.
The shield system facilitates the safe use of prefilled syringes, though it can be adapted for other sharp-pointed medical devices, such as syringes filled just before use, as well. When employed with a syringe, the system allows the contents of the syringe to be expressed in a conventional manner. Continued, and preferably increased pressure exerted by the user on the plunger rod following injection causes the syringe barrel to move axially, thereby axially displacing the shield. Such displacement causes release of the stop member, and the spring to move the shield over the needle of the syringe. Protection against needle sticks is accordingly provided.